1. Field of the Invention
The invention relates to a system with an internal combustion engine which has a heat transfer circuit, with a fuel cell and with a climate control unit which is accommodated in the heat transfer circuit of the internal combustion engine for heating and/or cooling of the interior of a motor vehicle, as well as to a process for operating such systems.
2. Description of Related Art
Systems of the type to which the invention is directed are used if a fuel cell is to be available as an additional energy source. The fuel cell is used, first of all, to produce electrical energy with which the various assemblies of the motor vehicle are supplied. In the reaction which takes place in the fuel cell, heat is released which must be dissipated so that the temperature of the fuel cell does not exceed an allowable upper boundary. Here, it is conventional to provide a separate heat transfer circuit for the fuel cell since the fuel cell is made as a separate unit. This separate execution of the fuel cell has the advantage that the fuel cell can also be used in stationary operation, and thus, can be operated independently of the operation of other components of the vehicle. In stationary operation, for example, the compressor of a climate control unit, or also a stereo system, light source and all those energy consumers which are conventionally supplied by the battery in stationary operation are operated via the fuel cell; however this is only possible for a relatively short time due to the limited capacity of the battery.
The climate control unit which is a component of the system is conventionally accommodated in the heat transfer circuit of the internal combustion engine so that the heat produced by the internal combustion engine can be used to heat the motor vehicle interior. After a vehicle with an internal combustion engine is started, it takes a certain amount of time until the climate control unit can satisfactorily heat the motor vehicle since, first, the heat transfer circuit of the internal combustion engine must heat up to such an extent that the heat which the climate control unit can transfer to the motor vehicle is adequately available. Moreover, in modern internal combustion engines, there is the problem that the efficiency of the engine is so high that the heat transfer circuit can make available only comparatively little thermal energy for heating of the motor vehicle interior.
Auxiliary heaters which additionally heat the cooling liquid in the heat transfer circuit during the starting phase when the internal combustion engine has not yet reached its operating temperature are known. Such a heater is used in order to bring the internal combustion engine more quickly to its operating temperature, and on the other hand, to make available heat for the climate control unit. In the normal operating state, when the internal combustion engine has reached its operating temperature, the heat output can be improved by operation of the heater.
International Patent Application Publication WO 02/075131 A1 discloses a system with an internal combustion engine and a fuel cell in which the exhaust heat of a fuel cell is used to heat the internal combustion engine at the same time. For coupling of the fuel cell and internal combustion engine in heat engineering terms, it is proposed that either they be structurally joined to one another so that heat conduction from the fuel cell to the internal combustion engine takes place, or that there be a common heat transfer circuit for the fuel cell and internal combustion engine. Here, it is also proposed that the fuel cell be operated independently of the internal combustion engine in order to separately activate an auxiliary air conditioning system, auxiliary heating or readiness operation. The problem here is that the internal combustion engine is heated at the same time. While this improves the starting properties of the internal combustion engine, it takes a relatively large amount of energy. Especially in operating situations in which the engine is to be preheated and the interior is to be heated, not only briefly before starting the vehicle but, for example, in trucks with sleeping compartments, where the sleeping compartment must be heated over a long time interval, the heating of the internal combustion engine demands considerable amounts of energy.
On the other hand, for cooling, systems and processes are known, for example, from published German Patent Application DE 199 27 518 A1 in which the compressor of the cooling circuit is supplied with energy by a fuel cell in order to thus be able to carry out stationary air conditioning of the vehicle interior. Use of a fuel cell as the energy supplier for a compressor has taken into account problems which occurred in conjunction with other stationary air conditioning systems, for example, when using latent storages. Since latent storages occupy a large volume and have a cooling duration which is greatly limited in time, their use is not suited in many cases.
Likewise, according to German Patent Application DE 199 27 518 A1 and the use of a fuel cell proposed there, the problems in electrical supply of a compressor by the motor vehicle battery should be solved. This is because, when using the motor vehicle battery as the energy supplier, the duration of cooling is also greatly limited, there even being the risk that, after completed stationary air conditioning, sufficient battery power for starting is no longer present.
It is furthermore known that an auxiliary air conditioning system can also be operated by the internal combustion engine of the motor vehicle when stopped or by an additional motor. However, of course, this also has the disadvantages that disturbing noise occurs, power consumption is high, and burdensome emissions are formed.
An air conditioning system in which a compressor is operated using a fuel cell thus offers a useful starting point for further developments. If in any case the air conditioning system is intended for use while driving and also when stopped, there are requirements which can only be met with difficulty at the same time. While driving it can often be necessary to dissipate high thermal output. In contrast, when the vehicle is stopped, for example, in the air conditioning of the sleeping compartment of a truck, what is important is to be able to air condition with low heat dissipation per unit of time over a long interval. Therefore, if a system is designed for stationary air conditioning, a fuel cell is chosen with correspondingly low output and a corresponding compressor; however, this would result in that the air conditioning could be inadequate while driving.
However, even if the fuel cell and the compressor were designed to be large enough, there would still be different requirements with respect to different situations or also with respect to different areas of the vehicle interior, so that for this reason, the problems would not be adequately solved.